1. Field of the Invention
The present invention relates to a flux-cored wire for gas shield arc welding, and particularly to a flux-cored wire for gas shield arc welding capable of reducing the amount of fume generation, which is suitable for welding of mild steel, high tensile strength steel, low alloy steel and the like.
2. Description of the Related Art
Recently, there has been a problem in lack of man power in the whole industrial field. In particular, the industries of steel-frame work, machine-making, and shipbuilding have been seriously short of welders, and have developed techniques for enhancement of efficiency, automation and robotic process for welding, and also have made efforts to improve the hard, dirty and dangerous welding work environments.
Because of lack of welders, flux-cored wires for gas shield arc welding have increasingly required in terms of (1) easy welding, and (2) high efficiency welding. In particular, metal based flux-cored wires have a feature of lowering the amount of slag generation in addition to the above advantages (1) and (2), and are expected to be more widely used. However, the wires of this kind have a disadvantage in making the welding work environments poor resulting from generation of a large amount of welding fume.
Techniques of reducing welding fume have been disclosed, for example in Japanese Patent Publication Nos. 1403569, 1572313 and 1572327. In particular, it is well known that the reduction of the contents of carbon and oxygen in a sheath is effective to reduce welding fume. However, metal based flux-cored wires are used with a high current (for example, 300 to 500 A) to obtain a high deposition rate, to thus exponentially increase the amount of welding fume generation. This drawback cannot be solved by the conventional techniques.
On the other hand, titania based flux-cored wires have a feature being low in the amount of spatter generation and excellent in bead appearance, and further being easily used for welding in all positions, so that they have been widely used in the industries of shipbuilding, bridge construction, and machine-making. However, on the other hand, the lack of welders has become severe because of the harsh welding environments at high temperatures and with a large amount of welding fume.